Many of the elderly are hearing impaired with the hearing impairment sufficient to have an adverse effect on their ability to understand speech. The proposed project examines various factors which may contribute to the speech-understanding difficulties experienced by the hearing-impaired elderly. The proposed project uses a cross-sectional approach to examine age-related differences in two primary aspects of the speech-understanding process: (1) peripheral encoding mechanisms; and (2) cognitive processing. In the area of peripheral encoding mechanisms, experiments will investigate haw much of the speech-understanding deficits of the hearing-impaired elderly can be explained by the loss of hearing sensitivity alone and the extent to which the encoded representation of the acoustic stimulus is degraded internally by the sensorineural hearing loss. Modeling of the internal degradation that accompanies sensorineural hearing loss for simple and complex acoustic stimuli, including speech signals, will also be performed. Age-related differences in the cognitive processing of speech will also be examined. It is generally hypothesized that degradation of the speech stimuli, whether degraded internally (processed through an ear with sensorineural hearing loss) or externally (noise, reverberation, synthetic speech), will place increased demands on higher-level cognitive processing of speech stimuli. It is further hypothesized that elderly hearing- impaired listeners have a general deficit in the speed of cognitive processing that interacts with the increased processing demands associated with the degraded peripheral input to produce severe speech-understanding difficulties in this population. The interaction of deficits in cognitive processing with degradation in peripheral input will be investigated through examination of age-related differences in primary and secondary memory and in the use of contextual information for internally and externally degraded speech.